Numerous research efforts have already demonstrated the potential for graphene to improve the efficiency of solar cells. Now a team of researchers in China has leveraged the remarkable properties of the wonder material to develop a new all-weather solar cell design that is able to generate electricity when current solar cells can't – when it's raining.
Amongst graphene's numerous impressive properties is its conductivity, which allows electrons to flow freely across its surface. When placed in an aqueous solution, this gives the material the ability to bind a pair of positively charged ions with a pair of its negatively charged electrons in what is known as a Lewis acid-base reaction. This property is exploited to remove lead ions and organic dyes from solutions and inspired a team led by Qunwei Tang to develop solar cells that generate electricity not only from the sun, but also raindrops.
Rather than being pure water, raindrops contain various salts that split into positively and negatively charged ions. When the water comes into contact with graphene, the positive ions bind with electrons on the graphene surface. At this point of contact between the water and the graphene, a double-layer of electrons and positively-charged ions forms, creating a pseudocapacitor. The difference in potential between the two layers is large enough to generate a voltage and current.
Laboratory tests using simulated rainwater proved out this theory. A prototype dye-sensitized solar cell to which a thin film of graphene was applied, was tested with slightly salty water simulating rain. It managed to generate hundreds of microvolts and achieve a solar to electricity conversion efficiency of 6.5 percent. The researchers believe that with further refinement, the process could become efficient enough to produce all-weather solar cells that can generate electricity, whatever the weather.
The team's paper appears in Angewandte Chemie International Edition.Source:
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